1. Field of the Invention
The invention relates to the unitary construction of a float valve and a latch sleeve for retaining a wiping plug in its final sealed position adjacent the float valve following the conclusion of a well cementing operation.
2. Description of the Prior Art
The great majority of subterranean wells have the bottom end of the casing anchored in the well bore by a poured in place annulus of cement. Additionally, those wells employing liners which extend below the well casing also employ cement to anchor the bottom portions of the liner in the well bore. In either event, whether a casing or liner is to be cemented in the well bore, it is conventional to provide a cement float valve in the bottom portions of the casing or liner to permit the unidirectional flow of cement slurry downwardly through the valve and out of the casing or liner, and prevent reverse flow of the applied slurry into the casing or liner.
The next step commonly employed is to run a wiping plug, having elastomeric flanges on its periphery, down through the casing or liner to remove the cementitous material from the interior walls and also to provide a seal above the float valve to prevent entry of drilling mud or other well fluids into the region occupied by the float valve.
In the prior art devices, a lock sleeve or collar was threaded into the interior of the casing or liner coupling which is positioned immediately above the location of the float valve. Such lock sleeve engaged an expandable ring on the wiping plug to prevent its upward movement from its sealing position. Such lock sleeve threadably engaged the interior threads provided in the coupling at their central portion and attempted to effectuate a seal with the bottom casing or liner member to which the coupling was applied, by compressing an annular mass of rubber or other elastomeric material against the upstanding end of the liner or casing and into the threads of the coupling (See FIG. 1). As is known to those skilled in the art, the central threaded portion of a standard coupling has no specifications applicable to the threads at that location. More importantly, the upwardly facing end of the casing or liner is devoid of any specifications and can have any configuration. As a result, it has been recognized that the field assembled seal effected between the lock sleeve and the upstanding end of the casing or liner section to which the coupling is applied has not been effective and has resulted in leakage in a great many instances. Such leakage has previously not been considered a serious matter since the well could have one or more float valves disposed below the lock sleeve and, so long as those float valves achieved a seal, there would be no passage for cementitous or other fluids to rise upwardly through the improperly sealed lock sleeve. Modern wells involving extreme depths, pressures and temperatures cannot tolerate any possibility of leakage around any component.